If the thought of a giraffe being decapitated, or of a rooster being smothered by a pillow, seems howlingly funny to you, “The Hangover Part III” will be your kind of movie. (The script adds a knowing wink to its bad taste by appending a dismissive line about PETA.) Still, cruelty to animals isn’t the picture’s main problem—it’s the cruelty to the people in the audience that really matters.

The first two installments in the series were huge successes at the boxoffice, of course, and so a third was inevitable. But there’s also been a precipitous decline in quality. The 2009 original was just an anarchic slob comedy, but it had some laughs. The 2011 sequel was pretty much a retread of the same plot with a shift in locale the only major change, and it managed to be both unfunny and borderline repulsive. This follow-up, penned by Craig Mazin (who contributed to the second picture), jettisons the alcohol-and-drug-induced amnesia premise that fueled the first two (until a totally disgusting postscript during the end credits) and opts for a lazy chase scenario instead. It’s the absolute pits.

The idea is that the four guys—Phil (Bradley Cooper), Stu (Ed Helms), Alan (Zach Galifianakis) and Doug (Justin Bartha)—are abducted by a gangster named Marshall (John Goodman), who was robbed of a fortune in gold bullion by the wild Chinese crook Mr. Chow (Ken Jeong) back in Part I. Now Marshall’s demanding that the buddies locate Chow, who’s just escaped from a Thai prison, and deliver him—and the loot—to him. He takes the unlucky Doug hostage, threatening to kill him unless the others do as he orders.

That sets off what’s supposed to be a wild and crazy series of events, but the episodes are so sloppily written and clumsily choreographed that they generate neither laughs nor thrills. Much of the problem arises from the decision to relegate Phil and Stu pretty much to the sidelines and focus instead on Alan and Chow. That’s good news for Cooper and Helms, who appear to be tired of this shtick and anxious to wrap it up (the former is given the movie’s most dead-on line when he says, “What the f*** are we watching?”), and though his character might be unlucky, Bartha is fortunate to disappear for most of the running-time.

But for the audience it’s no picnic. As characters Alan and Chow are simply creepy, and Galifianakis and Chow’s exaggerated mugging makes them all the worse. Some of what passes for humor in their dialogue is likelier to make your skin crawl than anything else, and a few of their scenes—when Alan interacts with the young boy who’s the son of Jade (Heather Graham), the nice-girl stripper from Part I, or when Chow goes bananas in the Caesars Palace penthouse—are really squirm-inducing. The same might be said of Alan’s romancing of a pawn-shop clerk (Melissa McCarthy, for some unfathomable reason the flavor of the month) that sets up the movie’s big finale (and that awful postscript). It’s meant to be lovably odd, of course, but misses the mark by a mile and winds up seeming merely strange and unsavory. (It also includes a bull-in-a-china-shop moment that reveals Galifianakis to be a curiously inexpert practitioner of slapstick.)

All of which points up Todd Phillips’ wayward way with his cast. He can’t even get a decent performance out of Goodman, who stole every scene in “Flight” but here is just a generic, stolid thug. (In fairness, Mazin gives Goodman absolutely nothing to work with.) Or from Jeffrey Tambor, who has a cameo as Alan’s understandably exasperated father (his scene leads to another tasteless bit at a graveside). Or from Mike Epps, another returnee (like Graham and Tambor) from the original, who plays his few moments on camera with a desperate frenzy that makes you think he realized how hopeless the material was.

But even he pales beside Jeong, whose grimaces, ear-piercing shrieks and other odd quirks make him insufferable even before he dons a parachute and goes flying through the skies over Las Vegas in a big set-piece, also involving characters dangling off tall buildings in some dim Harold Lloyd-inspired slapstick, that falls as flat as his character does. Even as a peripheral figure in the previous installments Jeong was an irritant; placed at center stage as he is here, he’s appalling.

“The Hangover Part III” isn’t even particularly good from the technical perspective, though it must have had a large budget. The visual effects are mediocre, and the camerawork by Lawrence Sher no better than adequate. But it must be admitted that Phillips manages most of the action sequences decently enough, and editor Debra Neil-Fisher keeps them moving well, though she can do little to hide the dead spots in the purportedly comedic scenes.

Oddly enough, despite the title the movie contains virtually no alcohol consumption; even the postscript presumes it rather than showing it. You, on the other hand, might want to reinforce yourself with a few belts before seeing the movie. And in all likelihood you’ll feel the need for a few more afterward, if only to forget.